Brief overview

Sherlock faces the consequences of his relapse, and his father arrives to try to fix the situation. Joan and Sherlock, trying to get back on NYPD's good side, search for a missing woman working the theory she was killed by her husband.

When Morland offers to use his influence to have Sherlock and Joan reinstated as consultants to the NYPD, Sherlock's mistrust of his father makes him question his motivation to help. Also, with no work offers coming in, Watson wrangles a gig with the FBI investigating a triple homicide in a top-secret research lab.

When Sherlock finds himself distracted by his father's ongoing presence in New York City, he offers to help Morland resolve a work issue in exchange for his prompt departure home. Also, Holmes and Watson's investigation into the double murder of two men who looked alike leads them into the world of facial recognition technology.

When Holmes and Watson investigate the murder of a fertility lab technician, they discover the woman had a secret personal life that leads them to multiple suspects. Also, the tables are turned on Watson when she's investigated by an NYPD detective.

When an archaeologist is murdered, Holmes and Watson believe the man may have been killed for what he discovered during his last excavation in a local landfill. Also, Sherlock's relationship with Alfredo, his friend and former sobriety sponsor, hits a rough patch.

writes a crime novel based on her work with Holmes without her knowledge, an underlying issue in their relationship is revealed. Also, as Holmes and Watson investigate a retired FBI agent's murder, they discover the man's death is connected to an unsolved case from the victim's career.

Holmes and Watson investigate a homicide in which the victim was murdered in a manner reminiscent of the crimes of an infamous, and already incarcerated, serial killer. Also, Sherlock and Joan tutor Detective Bell for a police sergeant's exam that would lead to a promotion and a post at another precinct.

Holmes and Watson search for a computer hacker responsible for three murders, including the death of a Russian billionaire who was visiting New York City. Also, Joan is surprised to receive a solo dinner invitation from Sherlock's father.

Holmes' tentative reconciliation with his father suffers a setback when Holmes and Watson discover Morland has been keeping a secret that threatens all of their safety. Also, Holmes and Watson investigate two murders connected to a for-profit college and its illegal recruitment practices.

Holmes and Watson must search for a killer without any physical evidence to aid them after a bomb is detonated in the New York City morgue. Also, Watson is suspicious when an NYPD detective she's in a grudge match with asks her to consult on a case.

Captain Gregson's colleague from Narcotics asks Holmes to orchestrate the perfect heist inside the heavily armed and virtually impenetrable compound of a drug-dealing biker gang. Also, when Watson assists Fiona Helbron, who helped her on a recent case, she makes a surprising discovery about Holmes.

Sherlock and Joan search for a murderer who used poisonous mushrooms to kill a botany professor and a group of the instructor's students. Also, when Joan is disturbed by loud noise next door, she discovers her neighbour, Trent, is renting out his home through a vacation site that caters to hard partiers.

When Holmes' investigation into the attempt on Morland's life pushes their strained relationship to the breaking point, the identity of Sherlock's mother is revealed. Also, when three gang members are murdered, Holmes and Watson are amazed when an elderly woman emerges as their prime suspect.

When Watson runs into Captain Gregson and his secret girlfriend (Virginia Madsen)

, a former NYPD officer, she inadvertently sets the couple's breakup in motion. Also, Holmes and Watson investigate the murder of a wealthy woman who left her considerable estate solely to a beloved dog.

In this adaptation of The Hound of the Baskervilles, venture capitalist Charles Baskerville is struck and killed by a truck while fleeing for his life from what a witness describes as a huge glowing animal. Charles's brother Henry believes it might have been murder and Sherlock thinks he may be next. Suspects include the CEO of Stapleton Innovations, who stands to inherit a fortune if both Charles and Henry die. Meanwhile, Dr. Hawes's work is suffering due to the psychological effects of the events of "Down Where the Dead Delight" and he's starting to self-medicate; Sherlock warns him that he'll go into a downward spiral if he isn't careful.

A comic book hero impersonator is found dead. This leads the investigation to the publisher and we learn that the creator's grandson is the editor of that comic. The grandson unabashedly voices his dismay over the fact that his grandfather was screwed out of his rights in the 1940s, to the irritation of his coworkers. The grandson and the dead impersonator knew each other; thus, the impersonator stopped the grandson from going ahead with his plan to kill all his coworkers, but got killed himself in the process. Meanwhile, Joan is exhorted by Morland to find a mole in his organization because an important deal fell through. Sherlock cautions Joan by telling her that Morland made the Russian hitman from a prior episode disappear from prison. Joan tells Morland she couldn't find the mole, but then recruits the mole to become a double agent inside Morland's organization.

The search for a missing doctor becomes a murder investigation involving drug traffickers and an exclusive bunker for wealthy survivalists. Meanwhile, Sherlock puts in extra effort for his relationship with Fiona to work.

As Sherlock and Joan investigate an armed robbery of an illegal high roller poker game, they run into Agent McNally from the NSA who is also interested. They all learn, that the robbery was used as a smokescreen, that involved planting a listening device in a secure room for diplomatic communication. They confront the dealer of this poker game who turns out to be a spy. Joan learns she has a half sister, Lin.

A woman exiting a gym enters the car she thinks is her rideshare and is subsequently shot and killed. This brings Sherlock's and Joan's attention to a murder in Connecticut for which they think the man convicted is innocent. The first murder turns out to be a crime of passion with the second a cover-up for the first. After a heated exchange at the beginning of the episode, Joan and Lin reconcile.

Sherlock and Joan are investigating an apparent carjacking with two deaths and many details not fitting the puzzle. This carjacking was staged by the intended target and the hitman, hired by the target's business partner, only to be hijacked by the target's wife. Meanwhile, Joan meets her frantic double agent in Morland's organization, who is worried that Morland is on to them. Morland makes a surprise visit to the brownstone. The episode ends with Marcus being called to an armed robbery in a diner with multiple victims, one of them the double agent.

Joan tells Sherlock about her double agent in Morland's organization. The two of them suspect Morland of ordering the hit in the diner, but the evidence is pointed in a different direction after the suspect confesses to another murder for hire by the same person two weeks earlier. An online survey created by this victim in order to change the future perspective on sentencing is found to be connected to another simultaneous crime in Geneva and a lab assistant selling information on the ones coming up as psychopaths to what she thought was the CIA. The name of the contact she gives alerts Sherlock to the involvement of his longtime adversary, Moriarty.

As Sherlock is reviewing known evidence, which leads him to the conclusion that, instead of the imprisoned Moriarty, someone else is wielding the scepter in her organization, Morland's office is bombed by the Russian hitman. This leads Sherlock to an obscure professor, Joshua Vikner (Tony Curran). Not only is he the caretaker of Moriarty's organization, he's also the father to her daughter. New evidence on the hitman surfaces, after which an angry Morland appears at the brownstone trying unsuccessfully to coerce Sherlock into giving up the name of the caretaker. The Russian hitman is arrested, but doesn't share any useful information. Sherlock notices corrosion on his belt and a distinct smell, illuminating which type of propellant was used in the bombing. This points the team to the upstate theft of a pesticide barrel and a missing person. Meanwhile, Vikner summons Sherlock to gauge interest in a possible truce with Morland. As the team prepares for an interview with the DA, the prisoner is assassinated in a murder-suicide by a rookie cop who turns out to be one of the psychopaths flagged in the DANTE survey. When Sherlock and Joan return home, they come face to face with a bomb identical to the first one.

Sherlock quickly disarms the bomb and deduces that it was not Vikner, but another member of his group who wants to dethrone him by killing them, thus breaking Moriarty's rule of not harming him and Joan. The two of them find out with help from Morland that the bomber is connected to an Iranian diplomat in the organization, Hashemi, who is bent on deposing Vikner as leader. They meet with her only to realize the enormity of the organization and to learn the reason why Morland was targeted by Vikner. Some in the organization, like Hashemi, wanted Morland as the new leader until Vikner played his hand. Sherlock, Joan, and Morland work together to frame Vikner for a federal crime, only to find out that he was tipped off by a contact inside the FBI and is in the wind. Morland, in an attempt to protect his son, then contacts Vikner, who thinks he's going to be able to kill off Morland. Morland, however, has allied with Hashemi, so Vikner is killed instead by her men. Morland meets Sherlock on the brownstone's rooftop, telling him that he has taken over leadership of the organization with the aim of dismantling the network from within and explaining to him that it was the only way to guarantee he would not lose his son. He also promises that the group won't have a presence in New York and prepares to return to London.